portant and useful kinds of machinery which hu man ingenuity ever contrived. The idea of making steam subservient to powerful mechanical operations, seems to have been first entertained by the Marquis of WORCESTER, in the reign of CHARLES II. of England. But little more was done, either by him, or during his time, than to speculate on the subject. It was not till the close of the seventeenth century that Captain SAVARY, an ingenious and enterprising man, actually erected several steam engines, and obtained a patent for what he considered his own invention. He afterwards improved and simplified his machines himself; but the improvements which they have undergone since the date of his, are still more numerous. For these improvements the world is principally indebted to Mr. NEWCOMEN, Mr. BEIGHTON, and above all to Mr. WATT, who, with an ardour, an acuteness, and a philosophic comprehension, which do him immortal honour, has so extended the principles of these machines, so increased their power, so successfully obviated the difficulties and inconveniences attending their operation, so accommodated their construction to peculiar circumstances, and carried the economy of steam, and, consequently, of fuel, to such an astonishing degree, that he may be ranked among the greatest mechanical geniuses and benefactors of mankind that the eighteenth century has produced. The application of steam to the purposes of cookery, and of propelling vessels on the water, is also to be ranked among modern inventions. To the latter of these objects several of our own countrymen have paid particular attention, and with promising success. And although it must be granted that formidable difficulties have arisen in the execution of all the plans hitherto proposed, yet to doubt of the practicability of ultimately overcoming these difficulties, can scarcely be thought either to gratify a mind of true philosophic enterprize, or to be worthy of such a mind. Late navigators and travellers have furnished valuable materials towards forming a theory of the winds. It must be acknowledged that nothing entirely satisfactory has yet been offered to the world on this subject. Still many facts have been brought to light; important discoveries have been made; and from the number and talents of the gentlemen who have been for some time engaged in exploring this dark recess of philosophy, still greater advances in our knowledge of it may soon be expected. Various instruments, which answer valuable purposes for measuring the direction, the force, and the velocity of winds, have also been invented, within a few years past, by Dr. LINN, Mr. PICKERING, and others of Great-Britain. These inventions have been denominated the Anemoscope, the Anemometer, &c. Finally, the doctrines of Acoustics have been very successfully illustrated, since the time of NEWTON, by various inquirers. Many facts relating to the velocity, the intenseness, and the general principles of sounds, have been established by numerous experiments. The capacity of different bodies, to propagate sound, has become better understood by the investigations of modern philosophers. Mr. HAWKSBEE, of Great-Britain, first showed that sound is propagated further in dense than in rarefied air; M. BRISSON, of France, and others, demonstrated, by various interesting experiments, that a medium more dense than air conveys sound still better than this fluid; and Dr. YOUNG, of Dublin, has, within a few years, made some new and instructive inquiries into the principles of acoustics. To which may be added the interesting experiments lately made, showing the H different intensity, and the variety of tones of sound, in different gases, by PRIESTLEY, CHLADNI, JACQUIN, PEROLLE, and others. OPTICS. In this science great improvements have taken place in modern times. In 1704 Sir ISAAC NEWTON first published his grand work on Optics; and although many of his most interesting discoveries were made and announced toward the close of the seventeenth century, yet the collection and publication of them, in a systematic form, was reserved to be one of the distinguishing honours of the eighteenth. How numerous and important these discoveries were, is generally known. He ascertained the different refrangibility of the rays of light; he made some progress in exploring the principles and laws of colours, which had been so little understood before his time; he first explained the physical cause, and laid down with mathematical precision, the general laws of the reflection and refraction of light; besides many other valuable, but less important additions to the science of optics. It must be acknowledged that his doctrines are by no means free from errors and defects; but these are few in comparison of their great merits; and have been chiefly corrected or sup plied by the labours of subsequent philosophers. Since the discoveries of NEWTON many important additions have been made to our knowledge of the nature and properties of light. The materiality of this substance, and the great velocity of its motion, were more fully illustrated and confirmed than they had been before, by Dr. BRADLEY and Mr. MOLYNEUX, in 1727. A few years. afterwards M. BOUGUER, a celebrated French philosopher, distinguished himself by his experiments and observations on the same substance; particularly on the laws of its reflection and refraction. On this subject, indeed, he is placed, by a very adequate judge, among the most eminent observers and discoverers which the eighteenth century produced." Another species of action of other bodies on the rays of light, producing what philosophers have called inflection and deflection, was suggested by our illustrious countryman Dr. RITTENHOUSE, but was first demonstrated by the ingenious experiments of Mr. BROUGHAM. From these and other facts, it appears that light is operated upon by material substances; that it is subjected to the laws of attraction, and, of consequence, possesses gravity. In the same sphere. of experiment and observation may be mentioned Dr. SMITH and Mr. MITCHEL, of Great-Britain, who made many valuable computations with respect to the intenseness, and the best mode of measuring this subtle fluid. The property which various bodies, both animal and vegetable, possess of imbibing and emitting light, has also been investigated with more success by modern philosophers than during any former period. To which may be added, that a multitude of facts of the most interesting kind, relating to the effects of light on animal, vegetable, and mineral substances, have been made known within a few years past; and the nature and principles of some of these effects ingeniously and satisfactorily explored. . See PRIESTLEY's History of Optics, 4to. London, 1772; from which many of the facts related in this sketch are taken. Those who have perused this work need not be informed, that it is a wery interesting one; and that the labours of Dr. Priestley, in collecting so many historical facts relative to the science of Optics, together with his own experiments, hints, and inquiries on the subject, entitle him to an honourable station among those who have deserved well of this science in the eighteenth century. Transactions American Philosophical Society, vol. ii. The theory and laws of vision have received very great elucidation during the last age. Bishop BERKELEY, in his Essay toward a Theory of Vision, published in 1709, solved many difficulties which had attended the subject, and threw much new light upon it. He distinguished more accurately than any who had gone before him, between the immediate objects of sight, and those of the other senses, which become early and insensibly associ ated with them. He first showed that distance, of itself, cannot be determined immediately by sight alone; but that we learn to judge of it by certain sensations and perceptions which are connected with it. He led the way, also, in pointing out the difference between that extension and figure which we discover by means of vision, and that which we perceive by touch. By means of these investigations and discoveries he enabled philosophers to account for many phenomena in optics, of which the most learned had before given very erroneous accounts, or acknowledged themselves unable to furnish any satisfactory so. lutions. About the same time some valuable experiments and instructive publications were made on the seat and principles of vision, by M. DE LA HIRE, M. LE CAT, M. BOUGUER, and several other French philosophers. To these succeeded the inquiries of HARRIS, PORTERFIELD, JURIN, SMITH, and still more recently of REID and WELLS. In particular, the very difficult question of apparent magnitude and distance has been treated with great ability by BERKELEY and HARRIS; the phenomena of single and double vision have been solved by several of the persons above mentioned; and many remarkable fallacies of Inquiry into the Human Mind on the Principles of Common Scuse, &c. |